All material is copyrighted and the property of mehlmanmedical.
Copyright © 2020 mehlmanmedical.
Privacy Policy and Terms and Conditions
Why did I group these together and skip over D? Because discussion of D is annoyingly lengthy and requires its own post.
Vitamin C (ascorbic acid / ascorbate)
Most important function on the USMLE is for collagen synthesis
- Vitamin C is necessary for collagen synthesis. More specifically, it is required for the hydroxylation of proline and lysine residues within preprocollagen.
- The hydroxylation allows for crosslinking between amino acid secondary structure (H-bonds) within the collagen, thereby strengthening it.
- Scurvy (vitamin C deficiency) results in weakened collagen and easy bleeding.
| Subperiosteal and perifollicular hemorrhages are specific to scurvy.
Bleeding from gums and an ill-appearing patient are also frequent vignette descriptors. Yes, “ill-appearing” sounds vague, but the USMLE will actually say that in question stems. |
For scurvy, be on the lookout for metaphyseal thickening and fragmentation around the epiphyseal plates, corkscrew-shaped hair, multiple fractures, bruised/swollen joints, petechiae, and iron-deficiency anemia.
| DO NOT confuse the presentation of scurvy with that of Menkes syndrome.
Scurvy presents with “corkscrew” hair, but Menkes presents with “kinky” hair and neurological/mental impairment. Ridiculous, but this is what the USMLE tests. And only in scurvy will there be a mention of blood around hair follicles (perifollicular hemorrhages). |
Required for catecholamine synthesis
- Catecholamine synthesis (i.e., dopamine, norepinephrine, epinephrine) is also dependent on vitamin C.
- This is because dopamine β-hydroxylase, which converts dopamine to norepinephrine, requires vitamin C.
Required for duodenal absorption of iron
- Vitamin C ferrireductase, which converts Fe3+ at the apical enterocyte membrane to Fe2+. Only the Fe2+ state of iron can be absorbed.
- Therefore, vitamin C is necessary for iron absorption and deficiency can cause iron deficiency anemia (at least in theory on the USMLE).
- You’ll often see combined vitamin C-iron supplements in pharmacies for this reason.
Hypervitaminosis C can cause calcium oxalate stones
- Just memorize it. Vitamin C toxicity can cause calcium oxalate nephro-/ureterolithiasis via ↓ pH of urine to favor crystal deposition.
- Patient taking high-dose multivitamin and gets shooting groin pain → CaOxalate stones from excess vitamin C. Mind-blowing.
- Toxicity can also cause iron overload (↑ absorption), at least in theory.
Vitamin E (tocopherol / tocotrienol)
Protects RBCs from hemolysis
- Vitamin E is an anti-oxidant that protects RBCs from hemolysis. In the event of vitamin E deficiency, hemolytic anemia can occur because of increased RBC fragility.
Hypervitaminosis E can cause bleeding diathesis
- Hypervitaminosis-E can lead to increased INR.
- It is hypothesized that vitamin E interferes with vitamin K function and can lead to bleeding diathesis in patients on warfarin.
Deficiency can cause neurologic dysfunction
- Vitamin B12 deficiency also causes neurologic dysfunction, but the vignette may also mention hemolysis, which is not seen in B12 deficiency.
- A point of distinction between B12 and E deficiencies is that the former results in subacute combined degeneration, where the dorsal columns, spinocerebellar tracts, and corticospinal tracts are affected. This exact pattern is not seen in vitamin E deficiency.
| Vitamin deficiency + neurologic dysfunction:
↑ MCV + ↑ serum methylmalonyl-CoA = B12 deficiency Hemolysis (↑ unconjugated bilirubin) + normal serum methylmalonyl-CoA = vitamin E deficiency |
—
